The speaker says, flatly and more than once, that the person they're addressing doesn't love them. What makes the statement hurt isn't anger but the evidence behind it: the speaker can cry in front of this person, and nothing happens. The other's heart "doesn't ache anymore." The word "anymore" suggests it once did, so the speaker is mourning a change, not just stating a fact.
The language is bare and short. The line "You don't love me" comes back like a verdict the speaker can't stop repeating, and "There is no other reason. / That is all." shuts the door on excuses or hope. Nothing is left to argue about. The final line, "That is how you really feel," sounds almost like the speaker is trying to convince themselves.
The mood is quiet, tired, and resigned. There's sadness here, but it's the numb kind that comes after pleading has stopped working.